1. Field of the Invention
The present invention relates to a process for producing thread-wound golf balls consisting of a core, a layer of rubber thread wound thereon, and a covering layer. More particularly, the present invention relates to a process for producing thread-wound golf balls, in which the starting end and/or terminating end of the rubber thread is fixed in an improved manner.
2. Description of the Prior Art
Thread-wound golf balls are conventionally produced by winding a rubber thread on a core and forming a covering layer thereon. The core may be a "liquid center" which is a rubber bag (center bag) filled with a liquid or paste, or it may be a "solid center" made of solid rubber. To wind a rubber thread on the core (center), it is necessary to fix the starting and terminating ends of the rubber thread. This is accomplished in several ways as follows. One method consists of winding a rubber thread 2 to 3 times around the core such that the starting end is held down by the subsequent turns of the rubber thread. Another method consists of bonding the starting end to the core surface with a drop of adhesive (Japanese Patent Publication No. 49985/1986). A further method employed in the case the core is a liquid center (which is frozen before winding) consists of dropping water on the starting end resting on the surface of the frozen core, thereby causing the water to freeze (Japanese Patent Laid-open No. 126470/1976). The terminating end may be fixed by passing it under the last turn of the rubber thread or by means of an adhesive (Japanese Patent Publication No. 49985/1986).
The above-mentioned methods pose several problems as follows. The terminating end passed under the last turn of the rubber thread is liable to become loose unless it is sufficiently long. On the other hand, an excessively long terminating end will project from the covering mold in the subsequent step, leading to rejects. Moreover, passing the starting or terminating end under the first or last turn of the rubber thread can hardly be automated; it has to be done by troublesome manual operation.
This problem may be solved by fixing with an adhesive; however, the use of an adhesive presents another problem. The adhesive takes time to cure. The adhesive is sticky and liable to attract foreign matter. The adhesive does not satisfactorily work on the frozen liquid center. The adhesive remaining on the core affects the performance of the golf ball.
Fixing with frozen water also presents problems. Water causes rusting and moisture condensation. Water vaporizes to adversely affect the winding machine. It can be applied to the liquid center only.
As mentioned above, the conventional methods for fixing the ends of rubber thread are not necessarily satisfactory from the standpoint of production efficiency and product quality. There has been a demand for the development of a new process for the efficient production of thread-wound golf balls of high quality.
The present invention was completed under the above-mentioned circumstances.